Our research objectives in this work are: 1) To define the mechanism of integration of SV40 and polyoma viral DNAs into the cellular DNA; what viral or host functions are involved in the recombinational event culminating in covalent integration and what are the molecular details of the recombination reaction. 2) To define the host DNA locations and nucleotide sequences into which viral DNA integrates in non-transforming infections (if it occurs), in transformation in vitro and oncogenesis in vivo. 3) To define the viral DNA sequence within which the integrational recombination can occur and to correlate this information with the transcriptional control of the integrated viral genes. 4) To develop SV40 and Polyoma DNA as transducing vectors for introducing and studying the expression of foreign (non-viral) genes in particular animal cells.